Gramvärvimine

Gramvärvimine is a differential staining technique used in microscopy to classify bacteria based on their cell wall composition. Developed by Danish bacteriologist Hans Christian Gram in 1884, it remains a fundamental tool in microbiology and clinical diagnostics. The process involves applying a series of stains and reagents to a bacterial sample.

The primary stain is crystal violet, which stains all bacterial cells purple. Iodine is then added as a mordant, forming a complex with the crystal violet. The critical step involves decolorization with alcohol or acetone. Gram-positive bacteria have a thick peptidoglycan layer in their cell walls, which retains the crystal violet-iodine complex, appearing purple. In contrast, Gram-negative bacteria have a thinner peptidoglycan layer and an outer membrane, which is disrupted by the decolorizer, causing them to lose the primary stain.

Finally, a counterstain, typically safranin (a red dye), is applied. This stains the decolorized Gram-negative bacteria red, while the Gram-positive bacteria remain purple, masked by the crystal violet. Therefore, Gram-positive bacteria appear purple or blue, and Gram-negative bacteria appear pink or red under the microscope. This simple yet effective method allows for rapid preliminary identification of bacterial species, guiding further identification and treatment decisions in clinical settings.